Tosefta zu Terumot 2:9

The landowner has the right to set aside tithes of untithed produce in the amount of the terumah of tithes that are in the tithes. Rabbi Yosei says, [in the case of] the landowner that separates terumah from tithes, what he has done is done.

But orlah and diverse crops (kilayim) of the vineyard (see Orl. 3:7) are [treated] the same for Gentiles in the Land of Israel, in Syria, and outside the Land (cf. Avodah Zarah 54b:6). But Rabbi Yehudah says, the [laws of] the fourth-year vineyard do not [apply to] a Gentile in Syria. And the Sages say, they do apply (Ter. 3:9). Said Rabbi Yehudah, it so happened with S'gabion (שְׂגַבְיוֹן not שביון) the head of the synagogue of Achziv, that he had purchased from a Gentile a fourth[-year vineyard] in Syria and had paid [the Gentile] money for it. And he came and asked Rabban Gamaliel, who had been passing from place to place [about whether such a vineyard is liable]. And [Rabbi Gamaliel] said to him, "Wait until [this situation] becomes [the subject of] halachah" (i.e., Rabban Gamaliel did not know the answer). They [the Sages] said to him [Rabbi Yehudah], "This is no proof [that such a vineyard is not liable]. Not only that, but [Rabban Gamaliel later] sent him [S'gabion] in the hand of a deaf-mute messenger (alt., "a secret message," see Lieberman), [stating,] 'What you did, you did, but do not teach [others] to do so.'"

[If there are] five collections [of produce] on the threshing floor, terumah [may be] taken from one on behalf of all, said Rabbi Yehudah. When is this? At the time that the major part (עיקר) of the [produce of the] threshing floor still remains. If the major part of the threshing floor does not remain, terumah is taken from each collection separately. One who brings produce inside his house, even though they are scattered (מְפוּזָּרִין, see Megillah 13b:18), he [may] take terumah from one on behalf of everything. [If there were] two piles that were heaped together (see Ter. 4:12), he takes terumah from each and every one. If had sacks of produce or rounds of fig cake or דוגיות of dried figs, we [may] take terumah from everything in one basket, and take tithes from one on behalf of the other.

We may take terumah from a stack [of grain] on behalf of a pile, but not from a pile on behalf of a stack.

Rabbi Eliezer says, we [may] take terumah from the pure on behalf of the impure (Ter. 2:1). Said Rabbi Eliezer, it so happened the threshing floors caught fire in Kfar Signah, and they took terumah from the pure on behalf of the impure. They said to him, what proof is that? Rather, [we should conclude] that they took terumah "from them on behalf of them" (i.e., from pure produce on behalf of other pure produce). Rabbi Ilai (אלעאיי not אליעזר per Lieberman) said in the name of Rabbi Eliezer, they [may] take terumah from the pure on behalf of the impure, even [when it comes to produce that is in] liquids. How is this done? Whoever pickles olives in [a state of] impurity and seeks to take terumah from them in purity, he brings a funnel whose mouth is not wider than an egg, and places it on the mouth of an amphora, and brings the olives and puts them inside [the funnel] and takes terumah, and [in this way] he is able to take terumah from the pure on behalf of the impure or the "earmarked" (המוקף, see Tos. Kifshutah). They said to him, nothing is considered "fluid" but wine and oil (see Y. Chal. II.3.9). Rabbi Yosei says, he who takes terumah from the impure on behalf of the pure, whether inadvertent or intentional, his terumah is [valid] terumah (see Y. Ter. VI.1.6). Said Rabbi Yosei, why should there be any difference between this case (i.e., taking terumah from the impure on behalf of the pure) and the case of taking terumah from the bad [quality] on behalf of the good (which is valid terumah (Ter. 2:6 ))?

[In summary,] we [may] separate terumah and tithes from the impure on behalf of the impure, and from the the pure on behalf of the pure, and from the impure on behalf of the pure, but not from the pure on behalf of the impure (contrary to Rabbi Eliezer above (and see Bava Kamma 115b:14)). Rabbi Nehemiah says, we do not separate [terumah] from the impure on behalf of the impure, but only as to demai. They said to him, behold, it says (Num. 18:28), "... and [they] are to give from them the contribution of God to Aharon the priest" (i.e., the Torah does not distinguish between pure and impure in relation to terumah).

[In summary,] we [may] separate terumah and tithes from the impure on behalf of the impure, and from the the pure on behalf of the pure, and from the impure on behalf of the pure, but not from the pure on behalf of the impure (contrary to Rabbi Eliezer above (and see Bava Kamma 115b:14)). Rabbi Nehemiah says, we do not separate [terumah] from the impure on behalf of the impure, but only as to demai. They said to him, behold, it says (Num. 18:28), "... and [they] are to give from them the contribution of God to Aharon the priest" (i.e., the Torah does not distinguish between pure and impure in relation to terumah).

One who separates terumah and tithes on Shabbat, whether unwittingly or intentionally, his tithes are [valid] tithes, and one who immerses [impure] utensils on Shabbat, whether unwittingly or intentionally, the immersion counts (contra Ter. 2:3 [invalidating intentional tithing and immersion on Shabbat]).

A seah of terumah that fell into one hundred [of chullin] and afterwards [the entire mixture] fell into [a second batch of] chullin of any amount, behold, it is permitted. A seah of terumah [wheat] that fell into one hundred [of chullin wheat], we do not subtract the zunim (an inedible type of wheat that grows among regular wheat) that is in it (i.e., it may count toward the one hundred). A log of clear wine that fell into one hundred logs of cloudy (i.e., unfiltered) wine, we do not subtract the sediment that is in it (i.e., in the cloudy wine). A log of cloudy wine that fell into into one hundred logs of clear [wine], we do not subtract the sediment that is in it (but see Yerushalmi, holding that it is subtracted in this case).